High-resolution CO and radio imaging of z ~ 2 ULIRGs: extended CO structures and implications for the universal star formation law
Abstract
We present high spatial resolution (0.4 arcsec, ≃3.5 kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at z ~ 2: two submillimetre galaxies (SMGs) and one submillimetre faint star-forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either ^(12)CO (J = 4→3) or ^(12)CO (J = 3→2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of ~ 2) for intermediate-excitation CO emission in z ~ 2 ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3 arcsec) combined Multi-Element Radio-Linked Interferometer Network-Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This 'matched beam' approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt–Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high- z star-forming galaxies.
Additional Information
© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 February 4. Received 2010 February 3; in original form 2009 December 3. This study is based on observations made with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). We acknowledge the use of GILDAS software (http://www.iram.fr/IRAMFR/GILDAS). This work also makes use of observations taken by the University of Manchester at Jodrell Bank Observatory on behalf of STFC, and the VLA of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under agreement by Associated Universities, Inc. We are grateful to the Great Observatories Origins Deep Survey (GOODS) team for use of their ACS data. We would like to thank the anonymous referee, whose comments and suggestions helped improve this work. We would also like to thank Mark Krumholz for his enlightening thoughts on the CO conversion factor. MSB and IS acknowledge the financial support of STFC and CMC thanks the Gates Cambridge Trust.Attached Files
Published - Bothwell2010p10433Mon_Not_R_Astron_Soc.pdf
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Additional details
- Eprint ID
- 18844
- Resolver ID
- CaltechAUTHORS:20100629-092653200
- Institut national des sciences de l'Univers (INSU)
- Max-Planck-Gesellschaft
- Instituto Geografico Nacional (IGN)
- Science and Technology Facilities Council (STFC)
- Gates-Cambridge Trust
- Centre National de la Recherche Scientifique (CNRS)
- Created
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2010-06-29Created from EPrint's datestamp field
- Updated
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2023-10-20Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)